It is widely believed that a vaccine capable of protecting against HIV-1 infection and AIDS will require immunogens that induce high levels of antibodies with potent neutralization activity against primary isolates of the viruses, irrespective of their geographical origin, subtype or genotype specificity a goal that current vaccine candidates fail to even approach. Therefore, identification of epitopes that mediate broad neutralization is important for rational vaccine design and development. Particularly important is the development of vaccine candidate antibodies to the Clade C sub-types, present in developing nations, compared to the predominant North American Clade B subtype, and comprising an emergent strain with world-wide relevance.
The HIV envelope is the predominant target of neutralizing antibodies in HIV-infected individuals. Some neutralization epitope clusters appear to be exposed at least partially on gp120 env protein of primary and/or monocytotropic isolates. Despite extensive studies, over 20 years, no immunogen capable of eliciting broad vaccine neutralization has been found. For this reason a vaccine against HIV infection has been elusive.
The specific invention involves identification of short sequences of gp120 which bind to the co-receptor CCR5 which identifies peptides capable eliciting antibodies with potent neutralizing activity for diverse HIV strains and peptides that are an important component of an immunization strategy for HIV-1 protection. Antibodies produced to these attachment sequences, comprising binding site peptide immunogens, are anticipated to confer protection against infection by the HIV virus, irrespective of strain, and are also expected to be therapeutic, that is their passive administration will reduce viral levels and provide clinical benefits in persons already infected with HIV
The neutralizing antibody response to HIV-1 infection. Anti-human immunodeficiency virus type neutralization antibodies first appear months after the viremia following initial infection. Early-arising neutralization antibodies are highly type specific. Neutralizing antibodies response may broaden later in infection (16) but usually remain poor and occur sporadically in the majority of patients, including long-term infected individuals.
Neutralization antibodies recognize the HIV-1 envelope glycoproteins, which consist of the gp120 exterior and gp41 transmembrane glycoproteins. The gp120 glycoproteins bind the target CD4 and chemokine receptors CCR5 and CXCR4. Antibodies have in a very few instances been raised to epitopes of the gp120 which are only expressed after gp120 forms a complex with CD4. It is believed that the actual co-receptor binding site, a desired vaccine target, only forms upon CD4 association with gp120. These CD4 induced (CD4i) antibodies block CCR5 and CXCR4 binding of gp120-sCD4 complex. The number of CD4i antibodies isolated from HIV-1 infected humans is low.
Most initial work with HIV-1 vaccines was directed at developing vaccines that elicited neutralization antibodies. These neutralizing antibodies have been narrow in their action and specific almost entirely to strains of the inoculating virus in animal models. These antibodies therefore are not of broad specificity and would not make good vaccine candidates.
Most successful vaccines block virus binding to its receptor(s), which for HIV are the co-receptors CXCR4 and CC5(1, 2). Thus the identification of the co-receptor binding site, a focus of intense scrutiny for the past 20 years, which has not been accomplished until now, would be expected to produce an immunogen capable of yielding the desired broad neutralization of diverse strains suitable for vaccine use.
The subject of this application, in part, is an antibody against a biologically active co-receptor binding site. This antibody showed potent inhibition of gp120-sCD4 complex binding to the CCR5 receptor in studies in vitro and antibodies raised to the proper peptide conformation induce broadly neutralizing antibodies which are therefore expected to provide protective immunity against HIV-1 infection. i.e. a vaccine.
In over more than 10 years, only a few human MAbs that mediate broad and potent neutralization of most HIV-1 isolates have been isolated. Two of these MAbs bind to the surface of gp120 (MAbs b12 and 2G12) (3, 4), and one binds to an epitope just proximal to the membrane spanning domain of gp41. MAb b12 recognizes a complex discontinuous epitope involving the C3-V4 region of gp120 and carbohydrate. MAb 2F5 binds to a linear epitope on the ectodomain of gp41; however, the simplicity of this epitope is deceptive and probably more complex than the six-residue linear sequence MAbs b12, 2G12, and 2F5 have shown in vitro neutralizing activity against a wide variety of primary isolates. All recombinant envelope-based vaccine candidates tested so far in clinical trials, even including epitopes known to mediate broad neutralization did not elicit significant neutralizing antibodies against primary isolates. The peptide based vaccine candidates also fail to elicit adequate immune response.
Homologous sequences to peptide DAPTA (Dala1-peptide T-amide, (5)) are present within V2 of numerous HIV-1 isolates (we have examined 4, 078 sequences). Our results with a polyclonal, and a purified IgG antibody against the peptide DAPTA, showed significant neutralization activity against primary and laboratory adapted strains, raising the prospect that the eight sequences from the carboxyl terminus of V2 domain, in close proximity to the bridging sheets represent a new neutralizing epitope.